Structural characterization of a marine diesel-degrading bacterial biosurfactant

Abstract Marine hydrocarbon-degrading bacteria play a pivotal role in natural oil-spill remediation and are increasingly being explored for biosurfactant production. This study investigates a marine isolate, ODB, cultivated using diesel as the sole carbon source, and evaluates its growth kinetics, biosurfactant production behavior, substrate degradation efficiency, and structural properties. Seed and fermentation profiling revealed a clear shift from exponential biomass formation to secondary metabolite synthesis, with biosurfactant production initiating at 48 h and reaching a maximum of 12.6 g L −1 by 144 h under controlled bioreactor conditions. Comparative studies showed markedly higher yields and diesel degradation efficiency (83.33 %) in bioreactor setups than in shake flasks, underscoring the importance of aeration and agitation. Extraction optimization revealed that drying the clarified broth prior to solvent extraction significantly improved biosurfactant recovery. Structural characterization using TLC, FTIR, and H1 NMR suggests the biosurfactant is an amphiphilic compound possessing aliphatic, aromatic, and amino-functional groups. Functionally, the biosurfactant reduced surface tension to 30 mN m −1 , exhibited strong emulsification activity (E 24 ≈ 60 %), and demonstrated antimicrobial activity against Staphylococcus aureus and Escherichia coli . These findings highlight ODB as a promising strain for bioremediation and industrial biosurfactant production, with potential for scale-up based on its robust biochemical and physicochemical performance.